Pavement and method of preparing same



Patented July 9, 1929.

umrao STATES GEORGE E. SOU'IEB, OI ANGELES, CALIFORNIA.

PAVEMENT AND METHOD OF PREPARING SAME.

Io Drawing. Application filed April 14,

My invention relates to road construction and it has especial reference to pavements and to a method of building the same.

The invention' relates also to a pavement composition and structure which may be laid as a complete unit in a continuous manner. Present day practices of laying pavements, particularly 'asphaltic pavements, involve building the same in sections at different times in order that the various sections may attain the degree of hardness necessary for stability and strength before application of another'section is made. I find thatthis sequent application of courses used in the 1 building of pavements with intervening periods of time, produces a laminated pavement by reason of which the pavement is not a homogeneous unit and hence is unable to withstand shocks and impacts of'traffic and temperature changes, under the influence of which the pavement becomes deformed, or cracks or otherwise disintegrates.

One of the chief objects of the invention therefore is to provide a method of laying a pavementin which the courses required for same may be laid in uninterrupted manner whereby a pavement may be produced that is complete and requires no subsequent attention, as is now the case where topping and finishing of a pavement is not accomplished until the priorly laid course has set.

Another object of my invention is to provide a homogeneous and uniform pavement in which the component parts of same constitute a composite whole with no lines of cleavage.

Other objects of the invention are to provide a pavement that will remain stable under all conditions; to provide a pavement that 40 will withstand shocks and impacts of trafiic; to provide a pavement that will maintain its surface contour under all conditions of use and will be proof against cracking and disintegration; to provide a pavement that is water 4 proof and to provide a pavement that will ofier a maximum frictional resistance to vehicle tires and therefore prevent slipping and skidding thereon.

According to present practices of building pavement ofasphaltic concrete, silt, rock dust and other powdered materials are employed as an interstitial filler. These materials known in the art as mineral fillers, are water absorbent. Because of the fineness of the filler, which is practicallyan impalpable powder, it is impossible so to commingle it with 1928. Serial No. 270,154.

an asphaltic product that each particle is coated and thus waterproofed. When this type of mineral filler is exposed, it will absorb water that .percolates or filters through the pavement, and the presence of water in the pavement composition causes its disintegra- The petroleum coke which I use is a byproduct resulting fromthe cracking of petroleum oils and shows approximately the following analysis: Y

. Volatile matter 20 to 25%.

Fixed carbon to Small amount of ash, moisture and sulfur.

I find that powdered petroleum coke when admixed, in manner, to be described, with other ingredients of a pavement composition, raises the softening point of the pavement to a considerable degree, strengthens it and renders it more stable. By reason of the powdered petroleum coke in the pavement composition and of the volatile matter contained in it, the pavement is less susceptible to temperature changes and is preserved against be coming brittle in cold or freezing weather, and hence the pavement remains stable under allconditions.

In constructing my new pavement, I first prepare a base, which may be of any approved type in point of thickness and mlneral aggregates used, but differing from known compositions in the use of ground petrbleum coke admixed with asphalt -The base which I prefer to use comprises about 30% of sand, varying from 80 mesh to 10 mesh; 60% of rock ranging from 10 mesh to 2 or 2% inch screen\5% of asphalt, preferably the steam refined variety, and 5% ground petroleum coke. Theseproportions are exemplary .merely and may be varied asrequired by different practices and conditions. In practice, the .asphaltic material is heated to a proper degree of fluidity, which occurs approximately at a temperature of from 250 to 450 F. The petroleum coke, ground to a fineness so that at least eighty per cent of same will pass through a two hundred mesh sieve, is

pare-d subgrade, spread over the same evenly to the required thickness and then rolled until compact and smooth. Upon the base thus prepared and laid, and while still warm, I.

then spread a layer of material that will waterproof the base and also provide an interstitial filler for the final course, presently described. This waterproof course or layer is preferably composed of approximately 80% of clean sand, ranging from 80 mesh to 10 mesh; 10% of asphalt, of the steam refined class and 10% of ground petroleum coke of the character heretofore explained. These ingredients are intimately mixed together while hot, until a homogeneous mixture results, in which the-sand particles are coated with the petroleum coke-containing asphalt. This mixture, to wit, of sand, asphalt and petroleum coke, while still warm and in mal-' leable condition, is then applied to the warm base course and evenly raked thereon to a required thickness, which is determined by the depth or thickness of the top or finish course, and which in actual practice will not often exceed one inch. It is not necessary that the layer thus applied be rolled, except very lightly for purposes of smoothing same. The thickness of this layer in any event should never be such that upon the rolling in of the finish course, the interstitial spaces between the mineral aggregates composing same become filled to the entire extent of their vertical depth. A

Finally I apply a course of material that will provide a non-skid finishing surface to the avement. This course conslstsof clean crus ed rock or clean gravel ranging in size preferably from one-half to three-quarters of an inch. It is first heated and then airblown asphalt or asphaltic cement is added which is also heated and which for my purposes has a penetration of less than fifteen degrees, District of Columbia standard, under 100 gram weight, for five seconds, and a ductility of less than ten centimeters.

This course of asphalt-coated rock or gravel or mixture of same is raked evenly upon the foundation, as afore described, and then subjected: to rolling pressure. During this application of pressure, the unrolled surface layer applied to the base is firmly united to the warm base, while the rock of the finish course is firmly embedded in the soft unrolled or lightly rolled surface or layer and pressed through the same onto the base. The asphalt coated mineral aggregates which compose the finished nonskid surface of the pavement, are as stated, embedded in and pressed through the unrolled intermediate layer while such layer is still in a malleable condition. Thereby the material composing this layer is caused to enter the interstitial spaces between the mineral aggregates for a portion of their vertical depth, leaving exposed a surface composed of asphalt coated mineral aggregates with interstitial spaces, while asphaltic coating on the bottom and sides of the mineral aggregates unites intimately with the intermediate layer. The asphalt coating on the mineral aggregates of the top or finished surface, which asphalt is of the air blown type, insulates the intermediate layer against the influences .of atmospheric changes and thereby insures the stability of the pavement. The course or layer between the two rock courses, that is the base rock course and the finish rock or gravel course, composed as described of sand, asphalt and ground petroleum coke, is in itself waterproof, and, by reason of its density and compactness, prevents filtering or percola-' tion of water throughthe same onto the base.

It provides a waterproofing and a union between the Wearing surface and base, e-nables the top rock to be firmly embedded, and provides a shock absorbing cushion between the two courses of rock without impairing in any wise the homogeneity of the composite pavement.

All the courses are laid in immediate sue cession and while the heat is still contained in the materials composing the pavement, making thereby a pavement that is a uniform structure, having no lines of cleavage, and possessing stability under heavy loads and ability to withstand the impact of traffic without losing its contour or cracking.

I call attention to the factthat the silt, rock dust, or other fine mineral a gregates composing a part of the ingre 'ents' of modern pavements, will and does under heavy trafficconditions, work up to the surface, eventually filling the spaces between the mineral aggregates of a top surface. A non-skid surface therefore soon is transformed into a slippery smooth surface. This is owing primarily to the use of a steam refined asphalt. It is impractical and almost impossible to use an air-blown asphalt with silt, rock-dust, and other fine mineral aggregates because a composition 'of this character soon becomes brittle and under traific vibrations, crumbles and disintegrates. It is therefore of considerable importance to obviate the use of these fine mineral aggr gates. And it is also of considerable advantage to use an air-blown as-l phalt. In the present instance, the asphaltic coating on the surfacing rock or gravel covers or surfaces the sublayer and therefore prevents the transfer of atmospheric heat to the sublaycr, the binding ingredient of which is a steam refined asphalt, while the air-blown asphalt on account of its higher softening point and non-ductibility remains practically unaffected by such atmospheric heat. Therefore creeping of the surface and softening of the intermediate layer is effectively prevented.

What I claim, is:

1. A payment consisting of an asphalt coated rock base, a waterproofing layer of asphaltic coneretecontaining powdered petroleum coke, and a surface of rock coated with air blown asphalt rolled in the layer upon the base.

2. A pavement composed of a. base, a waterproof composition on said base consisting of sand, asphalt and powdered petroleum coke, and a non-skid wearing surface united with said waterproof composition while in malleable condition. and consisting of mineral aggregates coated with air-blown asphalt.

3. A'pavement comprising a base composed of rock, sand, asphalt and ground petroleum coke; a waterproofing layer laid on said base and composed of sand, ground petroleum coke and asphalt, and a non-skid surface on said layer, said surface composed of rock coated with air-blown asphalt, the rock surface being rolled into and through said layer onto said base whereby the interstitial spaces between the rock of said surface are filled to a partial extent of their vertical depths.

4. The method of constructing an asphaltic pavement which consists, -first, in preparing a base composed of heated mineral aggregates, ground petroleum coke and asphalt,

laying the mixture upon a suitable subgrade and rolling the same until smooth; second, in applying a relatively thin layer of waterproofing material composed of mineral aggregates, ground petroleum coke and asphalt, to the surface of said base while still warm; third, in applying to said layer a course of heated mineral aggregates coated with airblown asphalt, and finally in subjecting said course of mineral aggregates to pressure to unite the various. courses and cause a portion of the waterproofing layer partially to fill the interstitial spaces between said rock aggregates. V f

5. A pavement composed of an asphaltcoated rock base, a relatively thin layer of a mixture of sand, dust and asphalt upon said base to waterproof the same, and a surface of rock coated with an asphaltic body pressed into said layer so that a substantial portion of the rock surface with interstitial spaces remains exposed above said layer to form a nonskid surface.

6. A pavement composed of an asphalt concrete base, a relatively thin noncreeping layer of a mixture of sand, dust and asphalt upon saidbase to waterproof the base and provide a binding medium and a surface of rock, coated with an asphaltic body, pressed into and through said layer, the rock forming such surface being of a size that a portion thereof when subjected to rolling pressure will become embedded in the intermediate binding layer and contact the surface of the base, and a substantial portion thereof with intervening voids will remain exposed above said layer to form a non-skid wearing surface, the respective courses being applied while hot thereby to form a homogeneous pavement.

In testimony whereof I have set my hand.

GEORGE M. SOUTER. 

